Apparatus for removing debris from thermoplastic materials

ABSTRACT

An apparatus for filtering thermoplastic synthetic plastic material has a screw ( 5 ) bearingly supported within a housing ( 1 ) for rotation around its longitudinal axis for the transport and preferably also plasticizing of the synthethic plastic material. This material is supplied to the screw ( 5 ) through an intake opening ( 7 ) into the housing ( 1 ) and leaves the housing ( 1 ) through an exit opening ( 8 ). The screw ( 5 ) is subdivided into two sections ( 9, 10 ) disposed one behind the other in axial direction. A filter ( 40 ) provided with penetration openings ( 25 ) is disposed in the flow of the synthetic plastic material that is disposed between these two sections ( 9, 10 ), which filter ( 40 ) is disposed within the housing ( 1 ) between the two sections ( 9, 10 ) of the screw ( 5 ) so that it subdivides the interior of the housing. The filter ( 40 ) is connected for common rotation with at least one of the screw sections ( 9, 10 ). At least one scraper ( 26 ) mounted in the housing ( 1 ) engages the upstream side of the filter ( 40 ) and strips off coarse impurities from the filter when the filter ( 40 ) is rotated and conveys the impurities into a collecting space ( 27 ) that is in connection with the interior of the housing.

BACKGROUND OF THE INVENTION

The invention refers to an apparatus for filtering thermoplasticsynthetic plastic material, having a screw bearingly supported within ahousing for rotation around its longitudinal axis for the transport andpreferably also plasticizing of the synthetic plastic material that issupplied to the screw into the housing through an intake opening andleaves the housing through an exit opening, for example a nozzle,wherein the screw is subdivided into two sections disposed one behindthe other in axial direction and wherein a filter provided withpenetration openings for the synthetic plastic material is disposed inthat flow of the synthetic plastic material that is disposed between thetwo sections.

An apparatus of this kind has become known (EP 600,924 B). Within thisknown construction the two screw sections are separated from each otherby a sealing section that is by-passed by the processed syntheticplastic material via a by-pass leading out of the housing. A filter isarranged in this by-pass by which impurities contained in thethermoplastic synthetic plastic material to be processed are retained.This known apparatus is well suited for fine-grained impurities if theydo not constitute too high an impurity portion within the syntheticplastic material. If, however, the synthetic plastic material to beprocessed contains coarser impurity fractions, for example small stonesor metal parts, such as bottle caps, paperclips, wire stitches or thelike, the filter and the filter channels of the known apparatus becomequickly blocked, so that the filter cannot accomplish its function.

SUMMARY OF THE INVENTION

The invention has as one of its objects to improve a construction of theinitially described kind so that filtering of coarse impurities can bedone reliably and at a low price without the filter being frequentlychanged. The invention solves this task by disposing the filter withinthe housing between the two screw sections so that it subdivides theinterior of the housing and is connected for common rotation with atleast one of the screw sections, and with a scraper carried by thehousing engaging the upstream side of this filter, which scraper scrapesoff coarse impurities from the filter when it is rotated and conveysthese impurities into a collecting space in connection with the interiorof the housing. This filter retains the coarse impurities so that thefilter is passed only by the synthetic plastic material and fineimpurities contained therein, if any. If the latter impurities areundesirable, a fine filter, for example of the initially describedconstruction or disposed at the end of the screw, can follow.

By continuously scraping off the coarse impurities with the scraper, theupstream side of the inventive coarse filter is kept free fromadsorption and deposits so that coarse impurities also do not block thepenetration openings of the filter, but are compulsorily continuouslyconveyed off into the collecting space. When the volume of thiscollecting space is sufficiently dimensioned, the apparatus can operatefor a long time without there being a danger of a breakdown because ofblocking of the filter.

It is known within an extruder for synthetic plastic material (EP689,918 A) to dispose a stationary fine filter within the housingbetween a supply screw and the extruder nozzle for the separation ofimpurities contained in synthetic plastic material, and to scrape offthe impurities collecting on the upstream side of the fine filter bymeans of a scraper rotating together with the screw. For the filteringof coarse impurities, this apparatus is not useful.

According to a further embodiment of the invention, the filter isdisposed at a member separate from the screw sections or constitutessuch a member. This is advantageous when manufacturing and, if desired,enables one to change over already existing plants in the sense of theinvention.

A particularly favorable construction consists within the spirit of theinvention in that the filter is provided with a shaft sectionconstituting the separate member, being disposed between the two screwsections and being provided with an annular flange having penetrationopenings, this shaft section being connected for common rotation on atleast one of its front ends with the neighboring screw section. Thisresults in a simple, easily exchangeable and reliable construction.Connection for common rotation can be made by a screw section, which hasthe advantage that this connection, if desired, can easily be detachedat any time, but if the direction of rotation of the screw sections andof the thread direction of this screw connection are efficiently chosen,in operation the screw connection is automatically tightened so that anundesired detachment is not possible.

A particularly favorable construction consists within the spirit of theinvention in that the shaft section at the upstream side of the filterhas a lesser diameter than at the downstream side. Thereby, at theupstream side of the filter there is a space for the impurities scrapedoff by the scraper.

Further, advantages are obtained if the penetration openings of thefilter have a cross-section that increases in the flow direction of thesynthetic plastic material. This avoids solid bodies entering into apenetration opening can be crammed in the penetration opening, therebyblocking the filter.

Another suitable construction consists within the spirit of theinvention in that the scraper is provided with a scraping edge engaginga cylindrical section of the filter, particularly a cylindrical sectionof the shaft section, which cylindrical section immediately neighborsthe upstream side ends of the penetration openings. Thereby, the coarseimpurities are compulsorily conveyed off in a continuous and reliablemanner.

A preferred embodiment of the invention consists in that the housing hasa central section surrounding the separate member and being detachablyconnected to its neighboring housing sections so that after dismountingthis central housing section, the separate member carrying orconstituting the filter can be put off the housing. Therefore, thefilter or the member constituting or carrying it, respectively,constitutes an easily exchangeable member, which results in advantageswhen replacing or cleaning.

Within the invention, the scraper can be disposed within a tubeconnected laterally to the housing, in particular to its detachablecentral section, which tube with its interior constitutes at least aportion of the collecting space. This results in a low-cost constructionbecause the members necessary for mounting the scraper at the same timeserve for confining the collecting space. Within this, it is suitable tomount the scraper adjustably within the tube in a directionperpendicular to the axis of the screw, in order to enable one to adaptthe position of the scraper to manufacturing tolerances and to wearoccurring during operation. In order to enable one to easily exchangethe scraper, when necessary, within the spirit of the invention the tubeis detachably connected to the housing, in particular to its detachablecentral section. Further, it is suitable if the tube has a detachableclosure cap, in particular a screw cap, at its end opposite the housing,because after detaching this closure cap the collecting space confinedby the tube is accessible for emptying or cleaning. The collecting spacecan be provided with a closure valve so that a preferably automaticemptying of the collecting space is possible during operation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an axial section through the inventive apparatus; and

FIG. 2 is a section taken along the line II—II of FIG. 1 in a somewhatenlarged scale.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The apparatus for filtering thermoplastic synthetic plastic material hasa housing 1 that comprises an intake section 2, a central section 3,coaxially disposed thereto, and an exit section 4, also coaxiallydisposed thereto. Within the housing 1, a screw 5 is bearingly supportedfor rotation around its longitudinal axis and is driven for rotation indirection of the arrow 6 by a drive means, not shown. The thermoplasticsynthetic plastic material to be processed is supplied to the screw 5through an intake opening 7 of the intake section 2 of the housing 1.The screw 5 conveys the synthetic plastic material within the housing 1toward an exit opening 8 disposed in the exit section 4, which openingcan be formed by an extruder nozzle. Preferably, the synthetic plasticmaterial is also plasticised during this conveyance. The screw 5 has twosections 9, 10 disposed one behind the other in axial direction, thesection 9 being disposed substantially within the intake section 2, andthe section 10 substantially being disposed within the exit section 4.The two screw sections 9, 10 are connected to each other for commonrotation via a separate member 11, and this by means of threadedtrunnions 12 or 13 provided at this member 11 or at the screw section10, respectively, which trunnions are screwed into correspondingthreaded bores 14 or 15 of the screw section 9 or of this member 11,respectively. The direction of the threads of these screw sections is sochosen that, when the screw 5 is rotated in direction of the arrow 6, noloosening of these screw connections occurs, but a tightening of them.

The member 11 constitutes a shaft section 41 connected for commonrotation to the screw sections 9, 10 and has two cylindrical sections16, 17 adjoining the sections 9 or 10 of the screw 5, the diameters ofthe sections 16, 17 preferably being equal to each other and also equalto the core diameter of the screw sections 9 or 10. The volutions 18 or19 of the screw sections 9 or 10 are continued on the sections 16, 17 ofthe member 11. The outer diameter of these volution continuations isequal to that of the volutions 18 or 19 of the screw 5, so that theinner diameter of the housing sections 2, 3 and 4 is always the same. Atthe transition locations of the volutions 18, 19 of the member sections16, 17 to the screw sections 9 or 10, steps of the screw volutions mayoccur, they are not disturbing. Conical sections 20 or 21 adjoin thecylindrical sections 16 or 17 and merge into cylindrical sections 22 or23, from which the section 22 has a greater length—measured in axialdirection of the screw 5—than the section 23. The two sections 22, 23are interconnected to each other by a flange 24 of the member 11, theouter diameter thereof being equal to the outer diameter of the screwsections 9, 10. The synthetic plastic material, if desired plasticised,can pass this flange 24 through penetration openings 25 disposed withinit. The penetration openings 25 are disposed along at least one circle,preferably along a plurality of circles, around the axis of the screw 5.In the embodiment shown, only one of these circles of openings is shown,the inlet openings of the penetration openings 25 of this circle beingdisposed substantially centrally between the periphery of the section 22and the inner wall of the housing section 3, when seen in radialdirection of the member 11. The exit openings of the penetrationopenings 25 preferably have their periphery flush to the cylindricalsection 23 of the member 11. Suitably, the penetration openings 25 havea circular cross section that enlarges in flow direction of thesynthetic plastic material. The size of the cross section of thepenetration openings 25 is so chosen that there results a filter 40 forcoarse impurity particles of the processed synthetic plastic material,in particular for bigger solid particles, as stones, metal clips or thelike. By the increasing cross section of the penetration openings 25 itis ensured that a solid particle that has entered a penetration opening25 cannot be clogged within the penetration opening 25.

The solid particles retained by the flange 24 collect at the upstreamside of the flange 24 and are taken along in the direction of the arrow6 when the screw 5 rotates, since the sections 16, 20, 22, 24, 23, 21,17 of the member 11 constitute a shaft section 41 rotating together withthe screw 5. This enables one to compulsorily convey off theseimpurities continuously by means a scraper 26 from the interior of thehousing 1 into a collecting space 27 in connection with the interior ofthe housing. This collecting space 27 is confined by a tube 28 screwedlaterally (with respect to the axis of the screw 5) to the centralsection 3 of the housing 1 and in connection via an opening 29 in thewall of the housing section 3 with its interior. This opening 29 isintersected by the scraper 26 which at its end disposed within thehousing section 3 is provided with two scraping edges 30 engaging theperiphery of the cylindrical section 22 of the member 11 and the flange24, so that the solid particles are continuously conveyed off also fromthis surface. As can be seen, when the screw 5 is rotated, the pointedend of the scraper 26 brushes over the penetration openings 25. Sincethis pointed scraper end is bent against the direction of rotation ofthe screw 5 (arrow 6, FIG. 2), a force component acts onto the solidparticles scraped off which tends to compulsorily convey these particlesout of the annular space 31 neighboring the penetration openings 25towards the collection space 27. This is supported by the centrifugalforce and by the pressure of following solid particles.

The scraper 26 is adjustably mounted in the tube 28 so that its positionrelative to the screw 5 and relative to the flange 24 can be adjusted,for example when assembling or for compensation of manufacturingtolerances or after re-sharpening of the pointed scraper end. For this,the scraper 26 has two elongated openings 32 (FIG. 2) which arepenetrated by two screws 33 with sufficient play, which screws togetherwith a clamping plate 34 clamp the scraper 26 to the wall of the tube28.

The tube 28 has on its end opposite the screw 5 a detachable closure cap35 formed as a screw cap which is screwed onto screw threads 36 of thetube. This results in a tight closure which efficiently avoids pressurelosses in the synthetic plastic material conveyed by the screw 5. Afterdetaching the closure cap 35, the collecting space 27 is accessible fromthe outside, for example for inspection or cleaning. The tube 28 isinserted into a recess 37 (FIG. 1) of the central section 3 of thehousing 1 and is screwed to the housing central section 3 by means ofscrews 38 (FIG. 2). If desired, a plurality of tubes 28 with scrapers 26mounted therein may be provided, distributed around the axis of thehousing 1.

Instead of the screw cap 35, each tube 28 may be provided with a valve50 by which the collecting space 27 can be emptied. An actuator 52 underthe control of an actuator control 54 can be provided for actuating thevalve automatically, for example hydraulically or pneumatically or bymeans of electromotive forces, for example in dependence on time, sothat the collecting space 27 can be emptied at predetermined timeintervals. It is also possible to automatically empty the collectingspace 27 in dependence on the pressure of impurity particles collectedin the collecting space.

To facilitate mounting and enable one to easily exchange the member 11constituting the coarse filter, the sections 2, 3, 4 of the housing 1are detachably connected with each other by means of screws 39 (FIG. 1)engaging flanges of the housing elements.

If the coarse filter 40 is already sufficient, no further filter isnecessary for cleaning the synthetic plastic material. However, it isfurther possible to place a finer filter in the flow of the syntheticplastic material following the coarse filter 40, when seen in the flowdirection of the synthetic plastic material.

The exit opening 8 must not be an extruder nozzle. For example, if thescrew 5 is no extruder screw but merely agglomerates the syntheticplastic material or merely conveys it, for example towards the inletopening of a housing of a further screw, if desired, formed by anextruder screw, then the exit opening 8 can be constructed and disposedin any desired manner, for example also on the side wall of the exitsection 4, therefore not axially directed as this is shown in FIG. 1. Inparticular, the latter construction will be given if the screw 5 isdriven from the exit-side end, therefore, in contrast to the dispositionaccording to FIG. 1, at which the (not shown) drive means of the screw 5are disposed at the inlet-side end thereof.

What is claimed is:
 1. Apparatus for removing impurities fromthermoplastic synthetic plastic material, having a screw bearinglysupported within a housing for rotation around its longitudinal axis fortransporting the synthetic plastic material from an intake opening to anexit opening of the housing, the screw being subdivided into first andsecond screw sections axially disposed one behind the other, a filterfor removing the impurities from the plastic material disposed insidethe housing and between the first and second sections so that itsubdivides an interior of the housing, the filter including penetrationopenings through which the synthetic plastic material passes and beingconnected for common rotation with at least one of the screw sections,and a scraper arranged in the housing positioned on an upstream side ofthe filter, the scraper being adapted to scrape off coarse impuritiesfrom the filter when the filter rotates and convey the impurities into acollecting space connected to the interior of the housing.
 2. Apparatusaccording to claim 1, including a member separate from the screwsections and wherein the filter is disposed at the member.
 3. Apparatusaccording to claim 2, wherein the member is separate from the screwsections and forms the filter.
 4. Apparatus according to claim 2,wherein the member comprises a shaft section disposed between the firstand second screw sections and forming the filter, and an annular flangeincluding the penetration openings, at least one end of the shaftsection being connected to an adjoining screw section for rotationtherewith.
 5. Apparatus according to claim 4, including a screwconnection connecting the at least one end of the shaft section to theadjoining screw section.
 6. Apparatus according to claim 4, wherein theshaft section upstream of the filter has a diameter that is less than adiameter of the shaft section downstream of the filter.
 7. Apparatusaccording to claim 2, wherein the housing has a central sectionsurrounding the separate member and is detachably connected to itsneighboring housing sections so that after removal of the centralhousing section the separate member and the filter can be removed fromthe housing.
 8. Apparatus according to claim 1, wherein a cross-sectionof the penetration openings increases in the flow direction of thesynthetic plastic material.
 9. Apparatus according to claim 1, whereinthe scraper is provided with a scraping edge engaging a cylindricalsection of the filter which is adjacent upstream ends of the penetrationopenings.
 10. Apparatus according to claim 9, including a membercomprising a shaft section disposed between the first and second screwsections and forming the filter, and wherein the cylindrical section isa section of the shaft section.
 11. Apparatus according to claim 9,wherein the scraping edge is bent against a direction of rotation of thescrew and defines a pointed end of the scraper.
 12. Apparatus accordingto claim 1, including a tube connected laterally to the housing andforming at least a portion of the collecting space, and wherein at leasta portion of the scraper is disposed within the tube.
 13. Apparatusaccording to claim 12, wherein the housing includes a detachable centralsection and the scraper is connected to the detachable central section.14. Apparatus according to claim 12, wherein the tube is detachablyconnected to the housing.
 15. Apparatus according to claim 14, whereinthe housing includes a detachable central section and the tube isconnected to the detachable central section of the housing. 16.Apparatus according to claim 12, wherein an end of the tube opposite thehousing is provided with a detachable closure cap.
 17. Apparatusaccording to claim 16, wherein the cap is a screw cap.
 18. Apparatusaccording to claim 12, including a valve associated with the tube foremptying the collecting space.
 19. Apparatus according to claim 18,wherein the valve is one of a hydraulically, pneumatically andelectromotively actuated valve.
 20. Apparatus according to claim 19,including means for activating the valve at one of predetermined timeintervals and a predetermined pressure of material in the collectingspace.
 21. Apparatus according to claim 1, wherein the penetrationopenings are arranged along at least one circle around the axis of thescrew.
 22. Apparatus according to claim 21, wherein the penetrationopenings are arranged along a plurality of circles arranged about theaxis of the screw.
 23. Apparatus for removing particulates fromthermoplastic synthetic plastic material comprising a screw rotatablysupported in a housing for transporting the synthetic plastic materialfrom an intake opening to an exit opening of the housing, the screwincluding first and second screw sections axially disposed one behindthe other, a filter for removing the particulates from the plasticmaterial, disposed inside the housing and between the first and secondsections, the filter including penetration openings extendingsubstantially parallel to an axis of the screw sections, permittingpassage of the synthetic plastic material and rotating with at least oneof the screw sections, and a scraper positioned on an upstream side ofthe filter for removing the particulates from an upstream side of thefilter as it rotates and conveying the particulates into a collectingspace.